Portable hoists have been used in a variety of industries for many years.
U.S. Pat. No. 2,418,813 granted Apr. 29, 1947 to Wallace W. Berchtold for "CRANE" discloses hoist-like apparatus especially adapted for removing and replacing heavy engines and wheels of buses. A hoist with somewhat similar mechanical features is described in U.S. Pat. No. 2,634,875 granted Apr. 14, 1953 to Raymond P. Trautner for "HOIST". The apparatus disclosed in this patent is intended specifically for raising and lowering meat carcasses in packing plants. The hoists in both of these patents utilize winch and cable mechanisms for raising and lowering the cargo.
U.S. Pat. No. 3,185,422 granted May 25, 1965 to Clemens E. Spindler for "COLLAPSIBLE AND ADJUSTABLE MACHINE FRAMEWORK CONSTRUCTION", No. 3,521,860 granted July 28, 1970 to Claude D. Zehrung, Jr. et al. for "KNOCK-DOWN HOIST", and No. 4,497,469 granted Feb. 5, 1985 to Richard W. Barnhouse for "VAN ENGINE REMOVAL ASSEMBLY" disclose hoists with pivotally mounted support arms that are actuated by hydraulic cylinders. Neither of these hoists, however has any provision for gross height adjustment other than the movable arm when the hoist is carrying a load. The Spindler patent provides for gross height adjustment, but without any mechanical advantage, so height adjustment with a load on the hoist would be cumbersome.
In positioning a hitch beneath a motor vehicle it is necessary to both lift the hitch and tilt the hitch, possibly about more than one axis. And because the hitch can be quite heavy the person installing the hitch usually requires mechanical assistance or the assistance of another person in effecting the different movements required of the hitch.
It is acknowledged that others have devised hitch-hoists capable of positioning and holding hitches beneath a motor vehicle. However, this prior art did not allow transverse angular adjustment and did not provide any mechanical advantage to allow longitudinal angular adjustments without operator support of the dead weight of the hitch. There continues to be a need for a hitch hoist which is simple and inexpensive in construction, can be employed by a single person to install a hitch with minimum exertion of effort and which is reliable in operation.